低圧縮比直接噴射式ディーゼル機関に高セタン価燃料を通常より早い噴射時期に高圧噴射し，その予混合気への火花放電によって噴霧の自着火を早期化・制御する新しい燃焼（SICI燃焼）に関して，その燃焼現象をボトムビュー可視化機関によって可視化し，圧縮自己着火誘発機構の解明を行った．その結果，50％蒸留温度が軽油より低いラウリン酸においては，適切な放電時期によって噴霧の自着火が早まる現象が確認できた．一方，比較的沸点が高い軽油ではSICI燃焼は観察されず，気化性の悪い燃料の場合は，量論混合気が形成されにくく，火花放電による科学種発生が生じにくいと推察された． The objective of this study was to visualize a novel combustion phenomena in which autoignition is induced by spark discharge into a premixture formed during a long ignition delay time in a direct injection diesel engine with a low compression ratio. the fuel used was lauric acid metyl ester that is relatively volatile and exhibits higher ignition quality than standard diesel fuel (gas oil). It was shown that spark-induced compression ignition, SICI, combustion was obtained with a low volumetric efficiency and at appropriate spark timing. However, SICI combustion was not observed in gas oil. These result suggest that relatively poor volatile fuel is difficult to form stoichiometric mixture around the spark plug. So that SICI combustion was not observed in case of gas oil.